Method of cleaning mercury boilers



252. COMPOSITIONS, UrOss iiBTGlGflCB 7 Exam,

June 26, 1934. A, J. NERAD El AL 1,964,594

METHOD OF CLEANING MERCURY BOILERS Filed Jan. 2s, 19::

Inventors:

Anthony. J' Nerad, Burt L.Newkir"k,

Their Attorney.

Patented June 26, 1934 UNITED STATES METHOD OF CLEANING MERCURY BOILERSAnthony J.

Nerad and Burt L. Newkirk,

Schenectady, N. Y., assignors to General Electrio Company, a corporationof New York Application January 26, 1933, Serial No. 653,650

12 Claims.

The present invention relates to methods .of cleaning mercury boilers ormercury vapor generators.

The capacity of a mercury boiler depends upon the heat transfer of thewalls of the boiler. This heat transfer is affected by the degree ofwetting of the boiler walls by the mercury. A mercury vapor generator inwhich the mercury does not wet the boiler wall has a much lower capacitythan one in which the mercury liquid wets the walls. To secure suchwetting it is advantageous to clean those heat transfer surfaces of theboiler which are in contact with the mercury to remove scale, slushingcompound, or other foreign materials so that the clean steel walls ofthe heat transfer surfaces may be brought into intimate contact with themercury. Since the erection of 'a mercury boiler with its associatedapparatus requires a period of months during which oxidation or otherimpairment of cleaned steel surfaces may occur before the mercury is putinto the boiler it is advantageous to use a cleaning process that can beapplied after the boiler has been erected and is otherwise ready to run.

Furthermore, in the operation of mercury boilers it has been found thatdeposits of iron, iron oxide and other substances are formed in theinterior of the boiler. These deposits decrease the heat transfer to theboiler and have other serious consequences, interfering with theoperation of certain parts of the boiler. This renders periodic removalof deposits necessary.

One object of the present invention is to provide an improved method ofcleaning mercury boilers either before and after they have been inoperation whereby mill scale or other impurities or foreign substancesas well as deposit formed during operation of the boiler may be removedfrom the heat transfer surfaces after the boilers have been erected and/or operated in the field.

For a consideration of what we consider to be novel and our invention,attention is directed to the following description and the claimsappended thereto in connection with the accompanying drawing in which wehave shown a typical construction of a present-day mercury vapor powerplant provided with certain elements for permitting the cleaning of theboiler in accordance with our invention.

The plant shown in the drawing comprises a furnace having a wall 10.Arranged within the furnace are a plurality of drums ll, 12 containingmercury liquid to be heated and evaporated. Connected to the lowerportion of each drum are a plurality of liquid circulating andevaporating tubes 13, each of which comprises an outer tube 14 fastenedto the wall 15 of the drum and an inner tube or core 16 projecting intothe drum and fastened to a baffle plate 18 arranged within the drum. Theinner tube has a passage 19 receiving liquid from the space above thebaflie plate. The lower end of passage 19 communicates with a space 20,hereafter termed vapor space, defined between the inner and the outertubes. During operation, the liquid flows through the liquid passage orspace of the inner tube into the vapor space where it is partlyevaporated and returned to the drum. A displacer block 21 is arrangedwithin each of the drums for displacing a portion of the liquid topermit operating the plant with a smaller amount of mercury liquid. Thedrums are connected to each other by liquid equalizing pipes 22 whichpreferably are arranged above the cold liquid level in the drums, asdisclosed in, the copending application of B. P. Coulson, Jr., filedDecember 29, 1932, Serial No. 649,350. In the present example we haveshown another liquid heating and evaporating element 23, having a header24 communicating with the drum or drums through a conduit 25. Theheating element 23 comprises down-tubes 26 connecting the upper header24 and a lower header 2'7, and up-tubes 28 arranged inside the furnacewall and connecting the lower header 2'? with the upper header 24.During operation, liquid is conducted from the drum or drums to theupper header 24, whence it flows through the down-tubes 26 to the lowerheader 2'1 and thence into the up-tubes 28 in which it is at leastpartly evaporated. The liquid expelled from the up-tubes 28 into theupper header 24 is recirculated and the vapor is conducted to the drumor drums. The drums are connected by conduits 29 and 30 respectively toa vapor supply conduit 31. The latter conducts the vapor produced in thedrums to a consumer, in the present instance shown as an elastic fluidturbine 32 having a valve 33 for regulating the'admission of elasticfluid to the turbine. The exhaust fluid of the turbine is condensed in acondenser 34 having cooling means 35. The condensate is returned to thedrum through a conduit 36 having branches 3'! and 38 connected to thedrums l1 and 12 respectively. Conduit 36, which may be termed a liquidsupply conduit, is preferably located above the cold liquid level in thedrums as disclosed by the aforementioned application of Coulson.

Our method for cleaning a mercury boiler comprises a plurality of stepsto be applied in their proper sequence. These steps apply both to 252.COMPOSITIONS,

' a moderate temperature.

.the boiler. with our invention by flushing the boiler with water. Inthe drawing we have shown two valves,

boilers to be put into operation and boilers which have been inoperation, with the exception of the first step, namely, the removing ofthe mercury from the boiler, which obviously applies to boilers onlywhich have been in operation.

A mercury boiler of the type described comprises a number of parts, suchas the heating units 23, and particularly the heating tubes 13 whichdefine spaces or dead ends from which the mercury cannot be drainedthrough valves. In cleaning a boiler which has been in operation weremove the mercury liquid by evaporation. The vapor thus formed iscondensed and stored in the turbine condenser or like containers. As theturbine condenser may be too small to contain all the mercury of theboiler, we may provide auxiliary containers. In the present instance wehave shown a container 39 having an inlet conduit 40 provided with avalve 41 and connected to the vapor conduit 31. An outlet conduit 43 forthe container 39 including a valve 44 is connected to the liquid header36. The container 39 is provided with cooling means 45 for condensingthe vapor conducted to the container. During the removing of the mercurywe maintain preferably a slow fire in the furnace to prevent overheatingof certain parts of the boiler. Maintenance of a good vacuum in theboiler during this step permits evaporation of the mercury at The valves33 and 41 are opened whereas valves-44 and a valve 49 in conduit 36 areclosed so that the vapor rising from the boiler is conducted through theturbine to the condenser 34 and through conduit 40 to the auxiliarycontainer 39. After the entire liquid is thus removed from the boiler,valves 41 and 33 are closed.

After the liquid has been removed from the boiler we fill the boilerwith a cleaning or pickling solution adapted to remove impurities ordeposits from the boiler walls. We have found that an acid solution,preferably a diluted solution of hydro-chloric acid attacks vigorouslythe scale, and other deposits on the interior of the boiler walls. Thesolution disintegrates, dissolves, undermines, and broadly speaking,removes the deposits within a comparatively short time. Tests have shownthat the application of a diluted solution of hydrochloric acid forabout two hours to the boiler walls is sufiicient to remove the depositstherefrom. The deposits are partly dissolved by the acid solution,forming compounds therewith, and partly maintained in suspension in thesolution. In the choice of the cleaning solution to be employed and thestrength of the .solution, care must be taken to adjust the factors oftime, temperature and strength of solution.

If the parts of a new boiler have all been cleaned thoroughly in theprocess of manufacture and .covered for protection with a greasy,slushing compound, such compound may be removed by a non-acid solventcleaning solution.

The next step of our cleaning method comprises the removing of thecleaning solution from This is accomplished in accordance one valve 46in the vapor conducting conduit 31, and another valve 47 forming a partof a conduit 48 connected to the liquid equalizing pipe 22 between thedrums. For removing the cleaning solution from the boiler, valves 46 and4'7 are opened and water is supplied through conduit 31 to the drums anddrained therefrom through the Cross .ieierence equalizing pipe 22 andthe conduit 48 connected thereto. While water is thus circulated throughthe drums and maintained at a level near the normal liquid level in thedrum, we maintain a slow fire in the boiler to cause circulation andagitation of the cleaning liquid contained in the heating tubes and theheating units in order to cause mixing of the cleaning liquid with thewater and to maintain small solid particles removed from the boilerwalls and not dissolved by the cleaning solution in suspension. With thecirculation of water through the drums and the circulation of the liquidcontained in the heating tubes and units the solution becomes more andmore diluted. This process is continued until the liquid is free fromcleaning solution. This can be easily tested by well known methods, forinstance, by means of blue litmus paper which turns red as long asliquid drained from conduit 48 contains acid.

The next step of our cleaning method is to remove the water from theboiler drums and replace it by mercury liquid. During this process carehas to be taken that no air comes into contact with the interior of theboiler which would cause oxidation of the walls. In accordance with ourinvention the water contained in the boiler is directly displaced bymercury liquid. The direct displacing protects the boilersurfaces fromair because the mercury liquid immediately contacts said surfaces as thewater is separated therefrom. With the arrangement shown in the drawingthis is accomplished by the opening of valve 44 in conduit 43 and thevalve 49 in conduit 36. The mercury liquid contained in condenser 34 andauxiliary container 39 thus flows through conduit 36 and its branches 37and 38 into the drums 11 and 12. The mercury liquid fiows first into theboiler tubes 13 and displaces the water contained therein and as soon asthe mercury liquid reaches the lower level of conduit 25 it fiows intothe heating unit 23 and displaces the water therein, the water beingdrained through the conduit 48. In view of the fact that conduit 22 ispreferably arranged somewhat above the cold liquid level in the drum andas water particles still cling to the interior wall of the drum, it isnot possible to remove all the water by displacing it with mercuryliquid.

The entire removal of the remaining portions of water forms the laststep of our invention which comprises the slow heating or drying of theboiler, preferably to a temperature between the boiling temperature ofwater and that of mercury liquid. During the slow heating the waterevaporates and the steam may be drained through the left-hand end ofconduit 31 which in a step heretofore mentioned served to conduct theflushing water to the boiler.

According to a modification of the step just described we add analkaline substance, for example ammonia, to the water used to flush outthe acid. This is to prevent oxidation of the steel surface between thepickling operation and subsequent operation of the boiler for generationof mercury vapor.

In accordance with a further modification of our invention we add to thecleaning or pickling solution a pic kl inginhibitor which may be anorganic substance such as g lue size or bran to slow down the actionof'the clearmfickling solution on the steel without affecting the actionof the cleaning solution on the deposits.

With our invention we have accomplished an improved method for cleaningthe boilers in Examine? mercury vapor power plants. Practice has shownthat these boilers should be cleaned before they are put in operation,as well as periodically during their operation. Summarizing, ourcleaning method comprises the following steps:

1. Removing the mercury liquid by slow evaporation, preferably at lowpressure (vacuum) in case the method is applied to a boiler which hasbeen in operation;

2. Filling the boiler with a cleaning solution;

3. Passing into and through the boiler (11111118 large quantities ofwater to flush out most of the cleaning solution;

4. Heating preferably at moderate vacuum the boiler tubes and heatingunits to cause circulation and agitation to remove the remainder of thecleaning solution and the deposits from the dead ends of said parts;

5. Directly displacing the water with mercury liquid; and

6. Drying the boiler at a temperature intermediate the boiling points ofwater and mercury to remove the remaining portion of water.

Having described the method according to our invention, together withthe apparatus for carrying out the method, we wish to have it understoodthat changes may be made in both the apparatus and the method withoutdeparting from the spirit of our invention and the scope of the appendedclaims.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. The method of cleaning a mercury boiler which comprises removing themercury liquid contained in the boiler by heating the boiler, placing adilute solution of an acid into the boiler, and then replacing the acidsolution by liquid mercury.

2. The method of cleaning a mercury boiler which comprises slowlyheating the boiler to evaporate and remove the mercury liquid containedtherein, placing a dilute solution of an acid for a definite time in theinterior of the boiler, and flushing the boiler with water.

3. The method of cleaning a mercury boiler which comprises placing adiluted solution of an acid in the boiler to subject the boiler wallsfor a certain period of time to the action of the acid whereby depositson the walls are removed therefrom, flushing the boiler with water toremove the acid and simultaneously heating the boiler to causecirculation and agitation whereby the water and the diluted solution aremixed and particles removed from the boiler walls maintained suspendedin the liquid, and then replacing the water with mercury liquid.

4. The method of cleaning a mercury boiler which comprises placing adilute solution of an acid in the boiler to subject the interior of theboiler walls for a certain period of time to the action of the acidwhereby deposits on the walls are removed therefrom, flushing the boilerby means of water to remove the acid, and directly displacing the waterwith mercury liquid whereby the boiler surfaces are protected from airbythe immediate replacement of the water by the mecury as the water isseparated from said surfaces.

5. The method of cleaning a mercury boiler which comprises filling theboiler with a dilute solution of an acid to the normal liquid level inthe boiler for removing deposits from the walls of the boiler, flushingthe boiler with water and simultaneously heating the boiler to removethe acid and deposits from the boiler, replacing the water with mercuryliquid, and drying the boiler by the application of heat to remove theremaining water therefrom.

6. The method of cleaning a mercury boiler having heating tubes whichcomprises filling the boiler with a dilute acid solution to the normalmercury liquid level in the boiler to remove deposits from the walls ofthe boiler, flushing the boiler with water and simultaneously heatingthe boiler until the acid is removed from the boiler, replacing thewater with mercury, and heating the boiler to a temperature intermediatethe boiling temperatures of water and mercury to remove the remainingwater therefrom.

7. The method of cleaning mercury boilers which comprises pouring acleaning solution into the boiler for removing deposits from the boilerwalls, flushing the boiler with water, directly displacing the waterwith mercury liquid, and drying the boiler whereby the boiler surfacesare protected from air by the immediate replacement of the water by themercury as the water is separated from said surfaces.

8. The method of cleaning a mercury boiler which comprises slowlyheating the boiler and maintaining a vacuum to evaporate and remove themercury liquid contained therein, pouring a cleaning solution into theboiler to remove deposits on the walls of the boiler, flushing theboiler with water to remove the cleaning solution, and replacing thewater with mercury.

9. The method of cleaning mercury boilers which comprises pouring adilute solution of acid into the boiler, flushing the boiler with adilute solution of a base to neutralize and remove the acid, flushingthe boiler with water, and directly displacing the water with mercurywhereby the boiler surfaces are protected from air by the immediatereplacement of the water by the mercury as the water is separated fromsaid surfaces.

10. The method of cleaning mercury boilers which comprises pouring adilute solution of acid into the boiler, flushing the boiler with adilute solution of ammonia to neutralize and remove the acid, flushingthe boiler with water, and directly displacing the water with mercurywhereby the boiler surfaces are protected from air by the immediatereplacement of the water by the mercury as the water is separated fromsaid surfaces.

11. The method of cleaning a mercury boiler which comprises pouring adilute solution of acid into the boiler, flushing the boiler with water,adding an alkaline substance to the last part of water, and directlydisplacing the water and the alkaline substance with mercury whereby theboiler surfaces are protected from air by the immediate replacement ofthe water by the mercury as the water is separated from said surfaces,the alkaline substance preventing oxidation of the boiler walls duringthe displacing of the water with mercury.

12. The method of cleaning mercury boilers which comprises pouring apickling solution including a pickling inhibitor into the boiler,flushing the boiler with water, and directly displacing the water withmercury whereby the boiler surfaces are protected from air by theimmediate replacement of the water by the mercury as the water isseparated from said surfaces.

ANTHONY J. NERAD. BURT L. NEWKIRK.

